Future semiconductor packages will be required to mount many highly integrated semiconductor devices, each with hundreds of circuits, on a single substrate, and interconnect these devices into an operative system. This will require that the area of the package be significantly increased, as compared to single device packages now in common usage, the wiring density increased, and that many closely spaced bonding terminals for connections to the semiconductor devices be provided. A structure that can potentially meet future high density package requirements is the multilayer ceramic substrate. In this substrate the metallurgy is buried within the substrate, making possible very complex and intricate wiring. This technology is well known and described in U.S. Pat. Nos. 3,540,894, 3,726,002, 3,770,529, 3,838,204, 3,852,877, 3,899,554, 4,109,377, and others. The basic process consists of forming a ceramic slurry of a particulate ceramic material, a resin binder, and a solvent for the binder, doctor blading the slurry and drying to produce ceramic green sheets, punching holes in and screening conductive lines on the green sheets, laminating the sheets, and sintering.
During the sintering step the substrate will shrink approximately 17% depending upon the materials, the sintering conditions, etc. This decrease in size can be accommodated by starting with a geometry that is larger than the final desired size by the amount of shrinkage. However, due to the relatively large size of the substrate, and the small geometry of the surface metallurgy, any variation of the shrinkage in the substrate presents serious problems in testing and in ultimately joining the devices to the substrate. If the shrinkage varies in different areas of the substrate, the substrate is frequently useless because of the resultant distortion.
Substrates are conventionally supported on a cured ceramic plate, typically Al.sub.2 O.sub.3 plate during the sintering operation. This sintering procedure has not been satisfactory for achieving uniform shrinkage in all areas of the substrate during sintering.